Which backpack size do you need? From 10 to 40 litres

One of the first questions when choosing a backpack is: how many litres do I need? Too small and your gear will not fit, too big and you lug around a half empty bag that sits awkwardly. In this article we lay out, per use, which backpack size makes sense, from a compact 10 litres to a multi day 40 litres.

We keep it concrete and free of manufacturer talk. The idea is that after reading you know which litre range fits your trips.

What do those litres actually mean?

The number of litres reflects the capacity of the backpack, meaning how much volume fits in it. It says nothing about comfort, fit or quality, only about space. A bigger bag is therefore not automatically better, it simply offers more room. The skill is choosing a size that matches what you actually carry.

10 to 20 litres: short trips and daily use

This size is ideal for short walks, commuting or a day out. There is enough room for water, a snack, an extra layer of clothing, a small first aid kit and some personal items.

• 10 to 15 litres: short walk, running, cycling
• 15 to 20 litres: day out, commute, light day trip

For anyone mostly out short and light, this size prevents you from carrying too much. Take a look at the more compact models in the outdoor backpacks.

20 to 30 litres: the versatile day trip

For a full day trip, 20 to 30 litres is often the sweet spot. You have room for a lunch, extra clothing for changing weather, a water solution, a medical kit and some spare items, without the bag becoming awkwardly large.

For many people this is the most used size, because it is broadly usable. How to pack such a bag smartly is covered in how to pack a backpack for a day trip or journey.

30 to 40 litres: long days and light multi day trips

If you walk long days, carry a lot or go away for a night, you quickly reach 30 to 40 litres. There is room for extra clothing, food, a sleep setup for light trips and more water. With this size pay extra attention to the fit and hip belt, because with more weight a good carry shape becomes more important.

For anyone looking for a sturdier, modular bag, the tactical backpacks are also worth a look.

How do you choose the right size?

Do not start with the bag, start with your use. Ask yourself these questions:

• how long are you out: a few hours, a whole day or several days?
• how much water and food do you carry?
• does the weather change, so you bring extra layers?
• do you carry delicate or bulky items?

A common mistake is buying too big "to be safe". A large bag tempts you to fill it up, leaving you carrying unnecessary weight. Better to choose the size that fits your usual trip and accept that an exceptionally long trip sometimes asks for a bit of creativity.

Frequently asked questions

How many litres of backpack do I need?

For a short trip 10 to 20 litres suffices, for a full day trip 20 to 30 litres and for long days or a light multi day trip 30 to 40 litres. Choose based on your use.

Is a 20 litre backpack big enough for a day trip?

For a light day trip 20 litres is often enough. If you carry a lot of clothing, food or water, you sit more comfortably with 25 to 30 litres.

Which backpack for a multi day trip?

For a multi day trip you usually choose 40 litres or more, depending on your sleep setup. In that case pay extra attention to the hip belt and the fit.

Is a bigger backpack always better?

No. A bigger backpack only offers more room, not more comfort. A bag that is too big tempts you to carry too much, leaving you needlessly heavy.